We've heard Osborne's plans to crack down on tax dodgers/ philanthropists (delete as appropriate), but what about higher rate payers and their charitable deductions?

Denise Van Outen holds a cheque for Great Ormond Street Hospital. But can she claim back the tax? Credit: Getty

The Financial Times is reporting that George Osborne is set to back down over proposals to limit the tax-deductability of charitable donations. The chancellor's planned cap on tax relief limited deductibles to the higher of 25 per cent of annual income or £50,000 per person, but the inclusion of relief given due to charitable donations in that cap sparked condemnation from all three parties and many charities.

As a result, Osborne is considering two new possibilities:

One plan is to have a separate limit on charitable donations of 50 per cent of a person’s income, allowing charities to claim tens of millions of pounds more in reliefs than under the current plan. Another is to let donors roll over any unused tax reliefs into future years if they are used for donations.

Treasury officials are locked in talks with representatives from the voluntary sector, and expect to make final decisions on how best to mitigate the effects of the planned cap in a few months. But they estimate raising the ceiling for charitable donations to 50 per cent would cost £40m, taking the overall savings from capping charities tax relief down to just £20m.

It is worth clarifying what the proposed changes are. Most of us are only aware of the most basic level of interaction between the tax system and charitable donations: gift-aid.

If a basic-rate taxpayer makes a donation, then a charity can claim back the tax paid on the money donated, boosting the value of the donation by 25 per cent (if the donor gives 80p, then the charity gets £1, which is the amount the donor had to earn to receive 80p post-tax income). There are no current plans to change that, and it has been an invaluable source of revenue for many charities.

If the donor is a higher- or top-rate taxpayer, however, tax relief kicks in for them as well as the charity. In addition to the 20 per cent gift aid, the donor can claim back the 20 or 30 per cent they paid on top of that, and count it against taxable income at the end of the year. So that 80p donation still earns the charity £1, but when the time comes to fill in their tax return, the donor won't have to pay more than basic rate tax on the money donated – they get 20 or 30p back. For a top rate taxpayer, that means that they are out-of-pocket by 50p, while the charity gets £1.

It is important to note that no-one makes money by donating to charity in this way. If the charity is a real one - and this whole affair was sparked because some people are apparently donating to bogus charities, which really is tax dodging - then the donor will always lose at least 50p in every pound the charity receives. It will indeed reduce the total tax they pay, but that reduction will necessarily be less than the amount they donate.

Despite that, there will be people using donations to avoid tax. It won't be rational, and it won't make them richer, but sometimes dodgers go to ludicrous lengths to not pay tax. Willard Foxton reported people "dodging VAT on cars by having them flown in at more cost than the tax". It is certainly believable that those who think like that would donate £2m to avoid paying £1m in tax; but it isn't going to be many.

Even for those who aren't donating out of blind desire to reduce their tax take, the cap will hit hard. Combined with other tax deductions, charitable donations may be enough to push the total tax-rate of a wealthy individual to less than 25 per cent. That is what is concerning charities. Under the proposed rules, the cost of donations to philanthropists with an already low tax rate will rise by 37.5 per cent. If donors react to that rise by donating less, then charities will be sorely hit.

The core issue at stake is whether or not charitable giving abdicates one's responsibility to pay for the machinery of state. On the one hand is the belief exemplified by Clement Atlee:

If a rich man wants to help the poor, he should pay his taxes gladly, not dole out money at a whim.

On the other hand is the belief that by donating to charity, one has fulfilled their responsibility to pay a "fair share".

In the real world the argument hasn't touched upon this morality much, if at all. Instead, the matter is presented in far starker terms; either a focus on "total tax rate" to the exclusion of the reasons why that rate might be low, or a focus on the total income of charities, to the exclusion of the source of that money.